1. Field of the Invention
This invention relates to mooring a floating vessel. More particularly, it relates to a mooring buoy which may be submersed to protect the buoy and associated submarine hose from extreme weather or sea conditions.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
Certain mooring systems of the prior art comprise anchored, floating buoys to which vessels may connect. However, such buoys are subject to whatever metocean conditions may exist at their location and are susceptible to damage from wind and wave action.
U.S. Pat. No. 5,431,589 describes a single-point submersible mooring buoy for use in ice-infested and severe sea state anchorages for transferring fluids between marine tankers and fluid handling facilities. The device includes a buoy body having a rotatable turntable disposed thereon for supporting a hose reel and a mooring hawser and associated winch. The buoy includes onboard anchor chain windlasses for maintaining anchor chain tension in the surfaced as well as submerged positions. Ballast tanks, compressed air reservoirs, hydraulic pumps and motors are disposed on the buoy and may be operated by remote control to move the buoy between floating and submerged positions and to provide for connecting and disconnecting the fluid transfer hose and mooring hawser with respect to a vessel such as a tanker.
U.S. Pat. No. 4,892,495 describes a subsurface buoy loading system for offshore oil gas production from production wells in the sea bottom. One or more flexible risers lead from the respective production wells to a submersible buoy adapted to be fitted to a complementary loading vessel in order to transfer petroleum products from the production wells via the loading buoy to the cargo space in the vessel. When not carrying out loading operations, the loading buoy may be descended down into an equilibrium position in the body of water. In the loading vessel, the buoy is fitted into a rotatable turret seat located in a downwardly open tunnel in the ship hull. The rotatable turret seat is positioned at such a level that the top side of the buoy, when in the loading position, is situated above sea level. The riser or risers extend through a vertical shaft in the buoy and are attached to the top of the buoy. The rotatable turret seat supports pipes communicating between the risers and a receiving pipeline system in the vessel.
U.S. Pat. No. 4,266,500 describes a compressed fluid hover control system for a submersible buoy in which the water level in a buoyancy chamber is controlled in accordance with external water pressure and predetermined levels of water in the buoyancy chamber. More specifically, a submersible buoy having a fluid-containing chamber containing a compressed fluid is connected to a buoyancy chamber by a gas inlet valve. A gas exhaust valve connects an upper portion of the buoyancy chamber to the surrounding water and a relief duct connects a lower portion of the buoyancy chamber to the surrounding water. Both the gas inlet and gas exhaust valves are controlled by a valve control circuit which opens and closes the valves in accordance with predetermined criteria related to water levels within the buoyancy chamber and the depth of the buoy as determined by a water pressure transducer. The valve control circuit thus causes the buoy to oscillate between predetermined depth levels, those levels changing as the compressed fluid is expended in order to maximize the operating life of the buoy.
U.S. Patent Publication No. 2004/0161303 describes a catenary anchor leg mooring system that includes a cylindrical hull portion which reduces the tendency of the cylindrical hull to roll and pitch in response to the action of winds and waves. This motion reduction is said to come from changing the diameter and draft of the cylindrical hull.
U.S. Pat. No. 6,062,769 describes a steel catenary riser system for use in an arrangement which includes a floating vessel such as a Floating Production, Storage and Offloading (FPSO) vessel floating on the sea surface and secured to the seabed by means of anchor legs which substantially prevent rotation of a turret which is rotationally supported on the vessel. The vessel is thus capable of weathervaning about the stationary turret under forces of wind, currents and waves. Steel Catenary Risers (SCR) run from the seabed sources of hydrocarbons to a Steel Catenary Riser Interface Buoy, called a “SCRIB”. A flexible riser hose, which may be suspended in a double catenary configuration, is coupled to each SCR at a SCRIB. The upper end of each flexible riser runs to the turret and connects to a fluid coupling (i.e., a swivel) and then via a pipe to a vessel holding tank. A cross-link is placed between two or more steel tubular lines in order to enhance the stability of the riser system. Devices are coupled to the steel tubular lines for increasing their tension in order to increase the natural frequency of vibration in order to reduce sensitivity to vortex induced vibration.